1 Level1 Central Track Trigger • Physics Justification • Proposed Implementation • Costs and Schedule Meenakshi Narain Boston University / Dzero Collaboration Run2b trigger meeting, April 25 th , 2002 Summary of work done in the Run2b L1CTT group Results from: Graham Wilson, Liang Han, Mike Hildredth, +input from Terry Wyatt, Marvin Johnson, Fred Borcherding, U. Heintz
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1 Level1 Central Track Trigger Physics Justification Proposed Implementation Costs and Schedule Meenakshi Narain Boston University / Dzero Collaboration.
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Level1 Central Track Trigger
• Physics Justification• Proposed Implementation• Costs and Schedule
Meenakshi Narain
Boston University / Dzero Collaboration
Run2b trigger meeting, April 25th, 2002
Summary of work done in the Run2b L1CTT group Results from: Graham Wilson, Liang Han, Mike Hildredth, +input from Terry Wyatt, Marvin Johnson, Fred Borcherding, U. Heintz
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Level1 Central Track Trigger
• Goals:– provide stand-alone track triggers– combine tracking and preshower information to
identify electron and photon candidates– generating track lists that allow other trigger systems
to perform track matching. • A critical part of the L1 muon trigger (current design)• Match tracks to L1 calorimeter candidates to identify
electrons and taus (proposed upgrade)• Used in Level2
– for identifying high pT electrons and muons candidates.– The L2 Silicon Track Trigger (STT) uses these tracks for
finding displaced tracks in the Silicon Microstrip Tracker which are from b-quark decays. The CTT therefore aims to provide tracks down to pT1.5 GeV.
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Current Run2a Implementation
• Uses Central Fiber Tracker and preshowers
• Divide into 80 sectors (each 4.5o)
• Track Finding:– Define hits from using pairs
of fiber in each axial layer (doublets)
– Compare doublet hits with predefined patterns to validate a track
Trigger response for Z ee MC with 4 min.bias overlayed
Red lines: triggered tracks from Z
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Why Upgrade?• Expected Run 2A performance:
– 97% of muons with pT > 50 GeV/c are reconstructed correctly
– Of the remaining 3%, 1.9% of the tracks are not reconstructed at all
– 1.1% are reconstructed as two tracks due to detector noise
• Expected Run2B performance:– Significantly more challenging due to increased number
of minimum bias interactions (4-5). – Tracking trigger rate is expected to rise dramatically due
to accidental hit combinations yielding fake tracks. – The 5 GeV threshold track trigger is satisfied in more
than 12% of beam crossings with 5 minbias interactions !
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Why Upgrade?• Run2b trigger rates with the current design are strongly
dependent upon the number of underlying minimum bias
• An increasingly compromised tracking trigger with luminosity!
Trigger rate for one track with pT > 10 GeV
Probability for specific track trigger terms to be satisfied in a given crossing
400KHz
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Paths for improvement…• A possible solution:
– The fiber doublet is larger than the fiber diameter, which results in a widening of the effective width of a fiber to that of a doublet, decreasing the resolution of the hits that are used for track finding.
– Use individual fiber hits rather than doublets
– Inherently narrower and therefore has a reduced probability of selecting a random combination of hits
Doublet Layer
1
2
3
4
Doublet Pitch
Minimum Bin Size
Fiber 1 Fiber 2 Fiber 3 Doublet
1 0 0 0
1 0 1 0
1 1 0 0
1 1 1 0
0 0 0 0
0 0 1 1
0 1 0 1
0 1 1 1
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Paths for improvement…• Use different schemes to get efficiency
and rejections. • Schemes:
– all-singlet case (16 layers)– mixed schemes
• some CFT layers are treated as pairs of singlet layers and the rest as doublets.
• Notation:– Upper case hits treated as doublets– lower case singlet hits. – ABCDEFGH : 8 layers of doublets
• Run 2a CTT scheme – abcdefgh: 16 layers of singlets.
Geometrical acceptance for hit requirement in the 16-trigger layer configuration. # of
hits
81112
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track sagitta, s = 0.02*e/ pT
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Different Equation SchemesDefault Doublet
Equations
16-Layer Singlet
Equations
12-Layer Equations
“abcdEFGH”
12-Layer Equations
”ABCDefgh”
14-Layer Equations abcdefGH
Efficiency for pT >10 96.9 99.3 98.6 97.3 99.2
Efficiency for 5< pT <10 91.1 97.8 92.8 90.8 91.6
Efficiency for fake pT >10 5.8 0.4 1.6 1.4 0.7
Efficiency for fake 5< pT <10 8.0 0.7 2.4 2.4 1.6
Fake TTK(2,10) 0.7 0 0.13 0 0.03
Fake TTK(1,5) 12.1 1.1 3.7 3.7 2.2
Fake TTK(2,5) 2.2 0.05 0.4 0.08 0.13
Single muons overlaid on events containing exactly six minimum bias interactions and put through the detailed DØ simulation and the modified trigger simulator.
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Diff Schemes: # of Equations
• Factor of 10 for 12singlets/2doublets• Factor of 4-5 for 8singlets/4 doublets
Singlet/Doublet Scheme Relative # of equations
Average number of terms/equation
All doublets ABCDEFGH 1.0 8
All singlets abcdefgh 15.3 12.6
2 doublets
12 singlets
abCdeFgh 10.5 11.4
ABcdefgh 10.0 11.4
abcdefGH 7.7 11.4
4 doublets
8 singlets
ABCDefgh 5.7 10.3
aBcDeFgH 5.6 10.2
abcdEFGH 4.2 10.2
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Effect of Inefficiencies• Inefficiencies tend to cause explosion in
number of equations.
• use npe=8, threshold=1.5
• For 16 singlet layer equations:Overall trigger
Efficiency
Fraction of equations kept(%)
Increase over Run2a terms
50 0.89 2.3
80 2.85 6.3
90 5.34 9.8
95 10.1 14.7
98 20.9 28
99 32 46.7
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A viable scheme
pT threshold
(GeV)
Efficiency Doublet /singlet scheme
Resources relative to total Run 2A resources
pT > 20 98% abcdefgh 28 x 1.5 x 0.075 = 3.15
pT > 10 98% abcdefgh 28 x 1.5 x 0.075 = 3.15
pT > 5 95% abcdefGH 6.2 x 1.4 x 0.2 = 1.3
pT > 1.5 95% abcdEFGH 3.0 x 1.2 x 0.5 = 2.5
•Use 16 singlet layer for high pT bin keeping high efficiency•Use 12 singlets and 2 doublet layers for low pT bins and accept lower efficiency•A factor of 10 more resources needed compared to Run2A
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Run2A L1CTT Implementation
J 0047
CFT AXAnalog
Front End(75 boards)
CFT AXAnalog
Front End(5 boards)
MIXER(20 boards)
DFEA
DFE Motherboard
DFEA
40 Motherboards,80 DFEA Daughterboards (1 per trigger sector)
DFE Motherboard
8 Motherboards
CTOC
DFE Motherboard
4 Motherboards
CTQD
DFE Motherboard
1 Motherboard
CTTT
Octant Boards Quadrant Boards
L1 Muon
DFE Motherboard
6 Motherboards
STOV
DFE Motherboard
6 Motherboards
STSX
L3L2CFT
L2CPS
to MTM
L3
L2
L3
System: 7 crates, 3 separate chains:axial tracker & central preshower